Aircraft cabins may become hot and stuffy, especially while flying at low altitudes in warm, sunny weather. When flying in other conditions, the cabin requires constant fresh air ventilation. In multiple seat aircraft, it is extremely important to supply the ventilation throughout the aircraft.
Ventilation supplied along the sides of the cabin is unsatisfactory, and a need exists for a system which will supply air in the center of the cabin and which will direct air to the places where it is desired.
Existing ventilation systems for small aircraft have air intakes on leading edges of wings, and air conduits leading from the air intakes inward within the wing and opening into an upper part of the cabin where the wing joins the body of the aircraft. The usual ventilation control is a telescoping slide-open, push-closed, turnable cylindrical valve, which is open at the end leading into the wing conduit, and which has an elongated rectangular opening in a side wall for controlling and directing air flow. The inner end of the valve is closed and may support a circular thermometer with an axial sensing probe to provide an outside air temperature gauge. Usually the face of the gauge is directed across the aircraft rather than toward the pilot, making the gauge difficult to read. Under darkened conditions or when flying at night, a flashlight must be used to read the gauge.
The movable cylinder usually has spring-loaded friction buttons which prevent overtravel of the cylinder into the cabin, and which glide along the inner surface of the wing conduit to hold the cylindrical valve in the selected axial extension and radial rotation so that none, all or a part of the rectangular opening opens into the aircraft. The cylindrical valve is turned to control the direction of flow and is pulled inward in the cabin to increase the flow. The flow is always along the side of the cabin. A deflector in the closed end of the valve attempts to deflect the flow angularly toward the middle of the cabin.
Cold air from the pull-open, push-closed, cylindrical vent valves tends to strike the outside shoulders of front seat occupants, blocking flow to the rear of the cabin and providing non-uniform flow over the front seat occupants.
Many problems remain with the use of the existing air vent controls for small aircraft.